Default Root on 4.4.2

Hi everyone.
I have 4.4.2 installed manually and now i want to get back the stock rom 4.2.2 because of a big touchscreen problem.
With flash tool, it always stopps at 15% so i have to flash rom with custom recovery.
The device is now unrooted, so i need a method to root KitKat. I tried already with iroot, vroot, kingo root, super one click root but none of them worked.
I need your help, thanks.